Process for preparing collagen fibers from tissue

ABSTRACT

The invention relaates to the production of collagen fibers by comminuting collagen containing tissues, drying the comminuted product and milling the dried material while maintaining the temperature sufficiently low to prevent substantial conversion of collagen to gelatin. The collagen fiber product is particularly useful for restructuring poorly textured meats, mechanically recovered meat products, offal, fish, fish products and other protein products to improve textural properties, water retention, fat retention, eating quality, juicines, succulence, shape, size retention and protein content.

The present invention relates to improvements in and relating to proteinproducts and in particular to the production of collagen fibers and tothe incorporation of collagen and collagen-containing compositions intoprotein products.

SUMMARY OF THE INVENTION

According to the present invention there is provided a process ofproducing collagen fibers which comprises, while maintaining thetemperature sufficiently low to prevent substantial conversion ofcollagen to gelatin, comminuting tissues containing collagen, drying thecomminuted product, and thereafter milling the dried material.

Furthermore there is provided a process whereby the collagen fiber thusproduced is added to protein products.

DESCRIPTION OF PREFERRED EMBODIMENTS

The tissues which may be used as starting material for the process ofthe invention include, for example, animal tissues including mammalianconnective tissue, sinews, dermis (split skin or corium after removal ofthe outer skin layers from hide or head hide), bird skins and connectivetissue, reptile skins and connective tissue, and fish skin andconnective tissue. Other sources of the tissues which may be used inaccordance with the invention comprise decalcificated bone dentine, andcollagen-containing tissues from the cardiovascular system, synovialmembrane, viscera, subcutaneous membrane, fetal dermis, vitreous humour,intervertebral discs, basement membrane, lens capsule, kidney glomeruli,placental membrane, and lung and muscle tissues. Preferred tissuesinclude mammalian connective tissues or sinews, such as ligaments,cartilage and tendon, for example, `Backstraps` or `Paddi wacks` fromcattle. Other preferred sources of the collagen used in the process ofthe invention are fish skins and the dermis of animals whose skins areusually consumed as food constituents, although bovine dermis is also apreferred source providing that its use is within the provisions of theprevailing food regulations.

The collagen fibers produced according to the present invention may alsocontain smaller quantities of other structural proteins, such aselastin, reticulin, connectin and desmin, and also mucopolysaccharideswhich are all naturally associated with collagen in varying amounts intissues.

Preferably, residual flesh and fats are manually or otherwise removed,for example by scraping, tumble abrasion or by soaking in salts such assodium chloride or in enzyme preparations such as papain. Solublenon-collagenous proteins and polysaccharides may be removed, if desired,along with a fraction of the soluble collagen, by soaking for example ina solution of sodium acetate, sodium dihydrogen phosphate or potassiumchloride. These procedures may also serve to remove other solublematerials present, such as glycans and saponified fats. Such solublematerials may also be removed, if desired, by soaking in saturated whitelime solution and thereafter removing excess calcium. Reducing the pHvalue to or towards the isoelectric point (pH4.6) for example to pH5.0,to provide enhanced storage stability in the treated tissue material maybe desirable following treatment with salt solutions.

Animal tissues rich in collagen, such as those collected from abattoirsmay conveniently be used immediately or be stored by freezing, forexample at minus 20° C., or by buffering, for example in a solution of aweak acid, such as citric acid, or in citric acid and sodium citrate, atfor example pH5.0, or by pickling, for example in a solution of sodiumchloride and a strong acid, such as hydrochloric acid or sulphuric acid.The source of the tissues is conveniently bovine, but othercollagen-containing materials, for instance materials from pigs, sheep,goats, game (including deer, eland and antelope), rabbit, hare,kangaroo, dog, monkey, camel, buffalo, horse, birds such as poultry(including chicken, duck, goose and turkey), pigeon and game birds,reptiles (including turtles and snakes), fish (including salmon, trout,eel, cod, herring, plaice, whiting, halibut, turbot, ling, squid, tuna,sardines, swordfish, dogfish, and shark), marine mammals (includingwhales), amphibians (including frogs), or crustacea (includingshellfish, crayfish, lobster, crab, shrimps and prawns) may also be usedas starting materials in the process of the invention. If pork (forexample from pig achilles tendon) or chicken (for example fromdefeathered skin or hen neck skin rich in collagen) or turkey (forexample from leg sinews) or other collagen-containing tissues are used,it is preferred that these have a low fat content. Where fat contentsare particularly high then fat rendering at low temperature (for examplebelow 60° C.) mechanically screw pressing, solvent extraction, with forexample, hexane, and treatment with lipase enzymes, such as fungallipases, may be advantageous.

It is preferred to carry out sample analyses of the cleaned tissues inorder to determine the protein (particularly the collagen content), fat,moisture, calcium, ash, heavy metals, pH value, and any microbiologicalcontamination. This is particularly preferred when the fibrous collagenproduced by the process of the present invention is required to be offood grade quality.

In accordance with the present invention, the tissue material iscomminuted, for example by being granulated, minced, cut, chopped, orground through a perforated plate, for example a 6 mm perforated plate.Conveniently, the material may be fed continuously into a grinder toproduce comminuted pieces, while ensuring that any temperature riseduring the comminuting process is kept to a minimum. Comminuting tissuestaken straight from a freezer, for example tissues which have beenmaintained at a temperature of minus 20° C., are preferred. It has beenfound convenient, for example, to arrange that the material iscomminuted into pieces of about five millimeters in diameter.

If desired, the comminuted product thus obtained may be pasteurized orsterilized, or treated to retard microbial growth, for instance bytreatment for a short period with dry high pressure steam, with hot fatsor oils or with ultra-violet light or ionizing radiation. Precautionsare preferably taken to ensure that the minimum of moisture and heattransfer occurs to the comminuted product during the pasteuriztion orsterilization. It may be advantageous to carry out sample analysis ofthe pasteurized or sterilized comminuted material after thorough samplemixing.

The comminuted material may be dried by using any suitable conventionaldrying or dehydrating means. Preferably the material is passed to thedrying stage with minimum delay, and especially within a period notexceeding 24 hours. The drying may be carried out by hot-air dryingprocedures such as in a tray drier or band drier, or drum drier, butother hot-air driers such as tube driers, paddle or tumble driers orfluid bed driers may be employed. Microwave driers, radio frequencydriers, or infra-red driers may also be used. Drying can also be carriedout in vacuum driers, extruders or in freeze driers, including forinstance by accelerated freeze drying and by freeze substitution. Dryingmay also be carried out using direct solar heating or in smoking ovens,when the product may also acquire a degree of microbial preservation andsmoke flavour. The comminuted material may also be dehydrated by usingfats or oils or in ethanol or other solvents.

If conventional hot-air drying of the comminuted material is employed,then the drying is preferably effected at a temperature up to andincluding 75° C., particularly at a temperature within the range from35° C. to 75° C. Within this range, drying at a temperature of from 45°C. to 55° C. is especially preferred. If a tray dryer or a tube dryer isused, the drying process is advantageously carried out within 24 hours,and preferably within 12 hours and the material may advantageously beturned occasionally, and preferably continuously, to facilitate evenheating and to obviate localized high temperatures. Rapid drying may befacilitated if relatively low loading densities of the comminutedmaterial are employed, for example from 5 to 10 kilograms per squaremeter, with an air speed of approximately 3 meters per second, the dryerbeing maintained at an air temperature of approximately 55° C. and at arelative humidity of approximately 40%.

If a fluid bed drier is employed, shorter drying times are preferable,and the temperature is advantageously maintained below 75° C. andpreferably below 60° C. If microwave drying, radio frequency drying,infra-red drying, solar heating, smoking, vacuum drying, extrusion, oraccelerated freeze drying methods are used, the temperature isadvantageously maintained below 75° C. and preferably below 60° C. Ifthe drying is effected by dehydration in fats or oils or other solvents,then a temperature of up to approximately 120° C. may be used, with thefat or oil or other solvent acting as a moisture-expelling solvent whileprotecting the collagen from being converted into gelatin as well asserving to reduce protein denaturization.

During the drying process, the moisture content of the material ispreferably reduced to less than 10% by weight.

The dried material is then milled in accordance with the presentinvention. A wide variety of conventional milling means may be employed.The use of a hammer mill or a pin mill is particularly preferred, bypinned disc mills, cross beater mills and turbo mills may be also beused. Advantageously the milling may be arranged to take place through ascreen for example through a 2.5 mm, 3.0 mm or 3.5 mm perforated screento produce a collagen fiber, or through a finer screen, for example, aperforated screen of 2.0 mm or less, to produce a finely dividedcollagen fiber. The product may thus have individual fiber lengths of upto 10 millimeters, preferably a fiber length within the range of from0.1 to 5 millimeters, and especially of from 0.1 to 0.5 or from 0.5 to 5millimeters, inclusive depending on the application. Any unground lumpspassing through the screen are preferably separated and recycled throughthe mill.

Any rise in temperature during the milling process is preferablymaintained at a minimum by careful control of the feed rate and by aircooling. However, it is particularly preferred that a coolant is addedto the material undergoing the milling if there is any possibility of asubstantial rise in temperature occuring. The coolant may be, forexample, liquid nitrogen or solid carbon dioxide.

At all stages in the process of producing collagen fibers in accordancewith the invention, the temperature is maintained sufficiently low topresent substantial conversion of collagen to gelatin. Preferably thetemperature is kept below a maximum temperature of 75° C.

Cyclones can be used to collect the product from the milling process,and the product may then be passed through a metal detector and weighedinto polyethylene containers.

It is advantageous to carry out sample analyses of the milled product,after thorough sample mixing. A typical analysis of bovine collagenfiber produced in accordance with the present invention is as follows:

    ______________________________________                                        Protein   92%                                                                 Fat       2.8%                                                                Moisture   5%                                                                 Ash       0.2%                                                                Arsenic   Less than one part per million                                      Lead      Less than one part per million                                      ______________________________________                                    

A further example of a typical analysis of collagen fibers produced inaccordance with the present invention is as follows:

    ______________________________________                                        Protein   85.7%                                                               Fat       2.3%                                                                Moisture  5.0%                                                                Ash       7.0%                                                                Arsenic   Less than one part per million                                      Lead      Less than one part per million                                      ______________________________________                                    

Percentages and parts stated are by weight. The protein may be collagenalone or it may contain other structural proteins naturally associatedwith collagen in varying amounts in animal tissues, such as elastin,reticulin, connectin, and desmin. A small amount of carbohydrate, in theform of polysaccharides naturally associated with collagen in animaltissues, may also be present. The bacterial specification of thecollagen fiber is preferably that of a substantially sterile material.

The collagen content of the material produced, or the content ofcollagen plus the other structural proteins generally present in thematerial produced, is preferably at least 85% by weight on a dry weightbasis, but it may be lower than this if other substances are present,for instance moisture, fat (including animal fats, vegetable oils andhydrogenated animal and vegatable oils), other proteins (including meatproteins, milk proteins, egg proteins, vegatable proteins such a soyaprotein, microbial proteins such as single cell proteins, and hydrolysedor autolysed vegatable or meat proteins), or other foods, foodingredients or food additives including cereals, carbohydrates such assugars, starches, modified starches, cellulose, modified cellulose andpectins, polyhydric alcohols such as glycerol, polyethylene glycol andsorbitol, gums such a xanthan gum, alginates and tragacanth gum, saltssuch as sodium chloride, sodium pyrophosphate and curing salts, spices,seasonings, flavourings and colourings. These additional substances mayact as dilutents, humectants, thickeners, or other functionalingredients in the meat or meat products, offals, fish or fish productsor other protein products or in cosmetic or medial products, comprisingthe collagen fibers produced in accordance with the present invention.

The collagen fiber produced may then be added, in accordance with thepresent invention, to protein products. The protein product or productscan comprise raw or cooked meat or meat products, offals, fish and fishproducts, and other protein products for food for human use, pet food,animal feed or fish food use, and also for use in cosmetic products andmedical products. The addition may be made by any of a wide range ofconventional mixing, adding, blending or compounding means.

Collagen fibers produced by any other method may also be added inaccordance with the present invention. Such methods comprise, forinstance, part extraction of collagen from animal tissues with (forexample) sodium citrate buffer solution of pH 3.7 to 4.3 andreconstitution into needle-like crystalline fibers by dialysis againstwater or diluted salt solutions such as disodium hydrogen phosphatesolution; bowl chopping, slurrying and extruding collagen containingtissues into fibers, followed by chopping and drying as required; andcell culture of collagen into formed fibers. These collagen fibers maybe added by the process of the present invention to protein productssuch as protein products for use as food for human consumption, petfoods, animal feeds, fish food, cosmetic products and medical products.

The collagen fiber is particularly useful for restructuring poorlytextured meats meat products, offals, fish, particularly comminuted fish(particularly comminuted meats), fish products, and other proteinproducts so as to enhance their textural properties, water retention,fat retention, eating quality, juiciness, shape and size retention, orconsumer appeal or to increase their meat content, fish content orprotein content, or to make more cost effective products. The enhancedappeal need not be only to the human consumer, but may also have greaterappeal to domestic pets when used in pet foods and to farm animals andfish when used in animal feeds and in fish foods.

Preferably collagen fiber from a particular animal species, includingindividual species of mammals, birds, reptiles or fish, is added to theproduct derived from the same species, but collagen fibers from anyparticular species can be added to the product derived from a differentspecies, whether mammalian, bird, reptile or fish, and also to proteinproducts derived from vegetable or microbial sources.

The following example illustrates the incorporation of collagen fibersin fish sticks in accordance with the present invention. 96 parts byweight of a frozen fish slurry of white fish, salmon or crab isdefrosted into a paddle type mixer, and 4 parts by weight of bovinecollagen fibers are streamed in while mixing. The temperature of thebatch is raised to 4° C. while mixing is continued, and the batch isthen immediately placed in moulds and frozen. The fish sticks thusproduced contain fish and added protein (beef collagen) for ingredientlabelling purposes. If fish collagen fibers are used instead of thebovine collagen fibers, then this would be included with the total fishprotein content and labelled accordingly. The fish sticks may bebattered and crumb coated as required, or precoated using finely dividedcollagen fibers and seasoned or coated with, for example, crumb,almonds, potato, dried fruit and sweet flavoured coatings.

Mechanically reocvered meat (MRM) is generally low in collagen becausegristles and matrix mucopolysaccharides are not incorporated.Consequently, the addition of collagen fibers to the MRM in accordancewith the present invention can bring the analysis of the product intoline with that of traditional meat cuts.

Incorporation of the collagen fibers is particularly advantageous forexample, in the formulation of burgers, where gristle-free meat ofapproximately 80% meat content can be converted into American-styleburgers with excellent juiciness and retention of shape by the additionof 4% bovine collagen fibers.

The following example illustrates the incorporation of collagen fibersinto beef burgers in accordance with the present invention. Rawdegristled forequarter beef (40% by weight) is minced and transferred toa paddle type mixer, and bovine MRM (45% by weight) and sodium chloride(1% by weight) are added and thoroughly mixed in. Bovine collagen fibers(4% by weight) are then streamed in while further mixing, and water (10%by weight) is added and mixed in thoroughly. The temperature is raisedto 4° C. and the mix is formed into any desired shape and size in pattieforming machines, and then immediately frozen. The ingredient list ofthe resulting beef burgers will be: beef, water and salt, and theanalysis will be 100% meat.

The MRM or other poorly textured meats (especially comminuted meats),meat products, offals, fish (especially comminuted fish), fish productsand other protein products can be raw, sterilized pasteurized, partlycooked or cooked before the collagen fiber is added to it in accordancewith the process of the invention. However, it is preferred that theproduct comprising the admixed collagen fiber, subsequently to theadmixture, is subjected to a cooking or heating procedure. In this waythe functional properties of the collagen fibers can be fully, orsubstantially fully, exhibited in the product of the invention.

The use of collagen fibers in accordance with the invention is alsoadvantageous in the production of continental-type sausages eithercooked (for instance frankfurters) or cured (for instance bierwurst).Addition of the collagen fiber may thus enhance the textural propertiesof the sausage products and act as a binder where non-meat binders, suchas soya derivatives, cannot be used because of legislation. In meatproducts incorporation offals, for instance hearts, the percentageincorporation of the offals may be increased and their texturalproperties improved by the addition of collagen fibers. Reformed meats,if formed from low-grade connective tissue products, such as raw orcooked MRM and offal, may be prepared with better cohesiveness and atlower cost by the incorporation of collagen fibers produced by thepresent invention. Fat retention in particular is enhanced givingimproved succulence and the addition of extra lipids, for instance meatfats, may also be assisted by the presence of the incorporated collagenfibers, resulting in a further improvement in juiciness.

In binding properties, for example in reformed meat and reformed fishfor foods for human consumption or for pet foods (particularly when MRMis used or when other comminuted meats or fish are used which have lostcohesiveness), incorporation of the collagen fibers can replace theaddition of non-meat or non-fish materials such as wheat gluten and soyaprotein, which are not universally permitted in Continental style cookedmeats, or of bovine plasma which cannot always be included within theofficially recorded meat content of the product. At the same time,textural properties, water retention, fat retention, eating qualities,juiciness, shape and size retention, meat or fish content and/orconsumer appeal may be substantially enhanced. Products formed byrestructuring offal proteins or bone proteins, for example byhigh-temperature extrusion or by deposition (for instance into alkali),may be further improved by incorporating collagen fibers in accordancewith the present invention.

Collagen fibers can be advantageously included in meat or meat productsto adjust the protein to total meat ratio to meet prevailinglegislation.

Meat products, fish products or other protein products which have beenpassed through a cooker extruder, with or without co-extrusion of pastryor potato or starches (for instance rice starch) to produce logs orcoated logs of cooked products in any of a variety of shapes, may besubstantially improved in as regards their textural properties, waterretention, fat retention, eating quality, juiciness, shape and sizeretention, meat or fish content, and/or consumer appeal by the additionof collagen fibers in accordance with the present invention. Similarformed products, produced in extruders through vacuum fillers via shapednozzles capable of substantially further compressing the product, mayalso be improved by the addition of the collagen fibers in accordancewith the present invention.

The incorporation of the collagen fibers into the protein product canadvantageously be combined with the addition of salts such as sodiumchloride, sodium pyrophosphate and curing salts to enhance still furtherthe binding properties, moisture retention or other desirablecharacteristics.

The incorporation of collagen fibers into meat or meat products can alsobe effected with advantage simultaneously with the addition of gums,preferably xanthan gum, to improve still further the textural propertiesand moisture retention during cooking. Such gums can be added by any ofa variety of conventional means, for instance by injection, tumbling,massaging or admixing. For example, if xanthan gum is used, the gumsolution preferably contains from 0.2% to 1.0% by weight of the gum.

In all the foregoing applications to which the collagen fibers of theinvention can be put, the collagen fibers appear to act in two majorways. Firstly, when mixed with other proteins such as mammalian muscleproteins in an aqueous environment they swell somewhat due to hydrationand, being fibrous and of optimum length, they phyisically bind thefibers of the muscle proteins together. On cooking or other subsequentheating or re-cooking, the shortening of the collagen fibers whichoccurs at a temperature in the range from about 55° C. to 65° C. as wellas the physical presence of the collagen fibers themselves causes theeating quality of the product to be greatly improved by introducing adegree of chewiness or texture into the product, thus simulating theeating qualities of a piece of steak. Secondly, they swell at highertemperatures and become softened as they take up water and partiallyconvert to soluble gelatin on cooking at about 70° C. to 85° C. thuscausing an improvement in tenderness. At the same time, and to a greaterextent on subsequent cooling, an increase in water retention andimproved perceived juiciness is caused by the gelling properties of thegelatin, giving an overall improvement in size and shape retention andenhanced eating quality. At cooking temperatures above 85° C. (internaltemperature) then increasing proportions of the collagen fibers areconverted into soluble gelatin, thus causing a further improvement intenderness but a reduction in the textural strength of the product.

The application of pressure while forming the products containingcollagen fibers is advantageous, for instance the use of plate freezers(for example at 5 p.s.i. at -40° C.), extruders (for example at up to 25p.s.i.) and particularly vacuum fillers under extrusion (for example at25 to 50 p.s.i.) ideally through shaped nozzles, especially the Z-bendconfiguration of extrusion nozzles. This may be due to a degree ofalignment of the fibers and of their layering in the most advantageouscases by the application of pressure in two directions and also to amore intimate binding of the collagen fibers and the meat or fishproteins for example under the application of the applied forces.

Collagen fibers in a finely divided state, typically with a fiber lengthwithin the range of from 0.1 to 0.5 millimeters inclusive, can beadvantageously used as, or as part of, a predusting system for proteinproducts, particularly meat products and fish products. For example, afinely divided collagen fiber (or powder) may be dusted onto a burgerand heated to allow partial conversion to gelatin, for instance bypassing it through a heated tunnel. Powder or granula coatings, such asspices, seasonings. flavouring, colourings, nuts, potato, dried fruit,sweet flavoured coatings and breadcrumbs, can be effectively bound tothe partially gelatinized collagen coating either by mixing them withthe collagen prior to the predusting stage of by adding them afterpartial collagen gelatinization. Thus the need to use a batter mix priorto addition of the coating is eliminated and with it the necessity toseal on the coating to prevent the migration of moisture utilizing, forexample deep fat frying. Finely divided collagen fibers can also beadvantageously utilized as a precoating system for protein productsparticularly meat and fish products and sealed by heating to allowbatter coating and enrobing with coatings such as crumb, potato and nutswithout the need for to further seal the product by for example deep fatfrying.

The present invention comprises collagen fibers when produced by theprocess of the invention.

The present invention also comprises protein products containingincorporated collagen fibers when produced by the process of theinvention. The protein of the products may be raw, pasteurizedsterilized, part cooked or cooked meat or meat products from mammalian,bird, or reptile sources, offals, fish or fish products, includingproducts derived from whales, krill or crustacea, or other proteins suchas proteins of vegetable or microbial origin, and products made fromthese proteins. The following example further illustrates the presentinvention. Raw mechanically recovered meat (MRM) is brought up intemperature from deep frozen to 1° C. and from 1% to 6% and preferablyapproximately 4%, by weight of collagen fiber produced for instance bythe process described in this invention is added portionwise and mixedthoroughly in a efficient blender, for example in a double arm typeribbon trough mixer. The temperature is brought up to 4° C., thepreferred maximum being 5° C., and the mixture is placed on freezertrays and plate frozen. On cooking or precooking at an internaltemperature of 65° C. to 100° C. (or from 115° to 125° C. for a shortertime in a pressure cooker or retort), the collagen fibers contact andthen partially convert to gelatin, thus binding the product together andimproving the eating qualities. At temperatures substantially above 80°C. the binding properties of the formed gelatin may be accentuated, butthe textural enhancement of the collagen fibers may be reduced.Conversion of the collagen fibers to gelatin is approximately 5% to 10%at 64° C. to 70° C., and 7% to 15% at 75° C. to 85° C. when held for ashort period. At 85° C. for a prolonged period, conversion may reach50%. At 100° C. conversion may be 10% to 20% when held for a shortperiod, and up to 100% when held for about 4 hours. Microwave heatingtends preferentially to increase the solubility of the collagen fibersrelative to the muscle proteins in meat, and hence lower internaltemperatures can produce levels of gelatin equivalent to that obtainedby higher internal temperatures produced by conventional cooking means.

The products thus produced may be used for example as replacement meancuts by slicing, as steaks by forming, and as Chinese stir-fryingredients or meat lumps for canned meats, pet foods, or soups, bydicing. A similar set of products may be produced if the raw materialused in the process is mechanically recovered fish, for instance fromdeboning processes.

In MRM and other meats and meat products and mechanically recovered fishand fish products, where the structure of the tissue has been destroyedand which on cooking is no longer able to prevent the egress of fluidreleased by proteins, collagen fibers can greatly increase water andlipid-holding capacities thus reducing `shrink` where it is derived fromboth aqueous and fatty sources, for example in cooked meats. In suchproducts, a further improvement in water-holding capacity may beobtained by the addition of gums, for instance xanthan gum andalginates, and of salts, for instance sodium chloride, sodiumpyrophosphate and curing salts. In this manner, loss of juiciness andpalatability is obviated.

The incorporation of collagen fiber into freshly prepared MRM as itemerges from the deboning machines, or after brief mixing to standardizebatches, can be highly advantageous as the MRM is at the optimumtemperature and its meat proteins are in the most available state tobind with the collagen fibers.

Irradiation of the collagen fibers, or of the collagen raw material, orof the protein product containing the collagen fibers, particularly ofthe collagen fibers produced by the process described in this invention,with sterilizing doses of ionizing radiation (such as 5M rad) may causean increase of tenderness of the product due to a decrease in the shrinktemperature of the collagen fibers.

Collagen fibers or finely divided collagen fibers can be advantageouslyused as carriers for flavourings, colourings and other food additives,particularly for use in meat products, fish products, and other proteinproducts, that are cooked prior to consumption.

Collagen fibers can be advantageously used as a source of protein and ofamino acids for nutritional purposes in food, pet food, and animal feed,and also in fish food, where the flotation properties of the collagenfiber in water can be combined with the flavour and colour carryingproperties of the collagen fiber in the formulations of complete fishfood preparations.

We claim:
 1. A process for producing collagen fibers from tissuescontaining collagen which comprises, while maintaining the temperaturesufficiently low to prevent substantial conversion of collagen togelatin, comminuting the tissues, drying the comminuted product andmilling the dried material, wherein said process produces a driedmaterial which is at least 85% by weight fiber protein.
 2. A processaccording to claim 1, wherein said dried material is about 85% to about92% fiber protein.
 3. A process as claimed in claim 1 in which residualflesh and fats are removed from the collagen containing tissue prior tocomminution.
 4. A process as claimed in claim 3 in which the residualflesh and fats are removed by scraping or by tumble abrasion.
 5. Aprocess as claimed in claim 3 in which the residual flesh and fats areremoved by soaking in a sodium chloride solution or an enzymepreparation capable of removing fat.
 6. A process as claimed in claim 3in which the residual fats removed prior to comminution are removed bylow temperature rendering, mechanical screw processing, solventextraction or by treatment with lipase enzymes.
 7. A process as claimedin claim 1 in which soluble non-collagenous proteins and polysaccharidesare removed from the tissues prior to comminution by soaking in asolution of sodium acetate, sodium dihydrogen phosphate or potassiumchloride.
 8. A process as claimed in claim 1 in which solublenon-collagenous proteins and polysaccharides are removed from thetissues prior to comminution by soaking in saturated white limesolution.
 9. A process as claimed in claim 1 in which the collagencontaining tissue is treated by at least one method selected from thegroup consisting of freezing, buffering and pickling, prior tocomminution.
 10. A process as claimed in claim 9 in which the collagencontaining tissue is buffered in a solution of citric acid and sodiumcitrate and pickled in a solution of sodium chloride and at least oneacid selected from the group consisting of hydrochloric acid andsulfuric acid.
 11. A process as claimed in claim 1 in which the collagencontaining tissue is comminuted by granulating, mincing, cutting,chopping or grinding through a perforated plate.
 12. A process asclaimed in claim 11 in which the collagen containing tissue is fedcontinuously into a grinder to produce comminuted materials whilemaintaining the temperature of the collagen containing tissue, up to amaximum of 75° C.
 13. A process as claimed in claim 11 in which thecollagen containing tissues are removed directly from a freezer at atemperature of at least -20° C. prior to comminution.
 14. A process asclaimed in claim 10 or claim 12 in which the collagen containing tissueis comminuted into pieces of approximately 6 mm in diameter.
 15. Aprocess as claimed in claim 11 in which the comminuted product ispasteurized or sterilized or treated to retard microbial growth.
 16. Aprocess as claimed in claim 15 in which the comminuted product istreated with dry high pressure steam, with hot fats or oils, or withultra-violet light or ionizing radiation.
 17. A process as claimed inclaim 1 in which the comminuted material is dried following comminutionuntil the moisture content of said material is reduced to less than 10%by weight, provided that said drying occurs within a period notexceeding 24 hours.
 18. A process as claimed in claim 17 in which thedrying is performed by using tray driers, band driers, drum driers, tubedriers, paddle driers, tumble driers or fluid bed driers.
 19. A processas claimed in claim 17 in which the comminuted material is dried using amicrowave drier, or a radio frequency drier or an infra red drier.
 20. Aprocess as claimed in claim 17 in which the comminuted material is driedusing vacuum driers, extruders or freeze driers.
 21. A process asclaimed in claim 17 in which the comminuted material is dried usingaccelerated freeze drying or freeze substitution.
 22. A process asclaimed in claim 17 in which the comminuted material is dried usingsolar heating or smoking ovens.
 23. A process as claimed in claim 17 inwhich the comminuted material is dehydrated by using at least onematerial selected from the group consisting of fats, oils, ethanol, andother solvents capable of dehydrating comminuted material.
 24. A processas claimed in claim 17 in which the comminuted material is dried in ahot air drier at a temperature within the range 35°-75° C.
 25. A processas claimed in claim 24 in which the comminuted material is dried at atemperature within a range of 45°-55° C.
 26. A process as claimed inclaim 1 in which the dried material is milled using a hammer mill, a pinmill, a pinned disc mill, cross beater or a turbo mill.
 27. A process asclaimed in claim 26 in which the milling includes the steps of passingthe milled material through a screen to produce a collagen fiber.
 28. Aprocess as claimed in claim 26 in which the milled product has anindividual fiber length of up to 10 mm.
 29. A process as claimed inclaim 26 in which the milled product has individual fiber lengths withinthe range 0.1 mm -5 mm.
 30. A process as claimed in claim 26 in whichthe milled product has milled fiber lengths within the range 0.1 mm -0.5mm.
 31. A process as claimed in claim 26 in which the milled product hasa milled fiber length within the range 0.5 mm -5 mm.
 32. A process asclaimed in claim 26 in which a coolant is added to the material tosuppress any rise in temperature.
 33. A process as claimed in claim 1 inwhich the collagen containing tissues are selected from the groupconsisting of animal tissues including mammalian connective tissue,sinews, dermis, bird skins and connective tissues, reptile skins andconnective tissues and fish skin and connective tissues.
 34. A processas claimed in claim 32 in which the collagen containing tissues areselected from the group consisting of decalcified bone dentine, collagencontaining tissues from the cardiovascular system, synovial membrane,viscera, subcutaneous membrane, fetal dermis, vitreous humour,intervertebral discs, basement membrane, lens capsule, kidney glomeruli,placental membrane, and lung and muscle tissues.
 35. A process asclaimed in claim 34 in which the collagen containing tissues includemammalian ligaments, cartilage and tendons.
 36. A process as claimed inclaim 32 in which the collagen containing tissues include fish skins andthe dermis of animals.
 37. A process as claimed in claim 33 in which thecollagen containing tissues include bovine dermis.